ndb_redis: add sentinel support to reconnection logic

[cruzccl]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

This PR replicates sentinel logic added in initial redis connection (via cc8e621) into reconnection function.

This way, in case of loosing connection with Redis, Kamailio will be able to reconnect to redis asking to sentinel servers defined in modparams.

[miconda]

Thanks!